# NOMA-Assisted Multiple Access Scheme for IoT Deployment: Relay Selection Model and Secrecy Performance Improvement

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## Abstract

**:**

## 1. Introduction

- Targeting the secrecy outage constraint, we comprehensively study the design of NOMA-assisted IoT system against the external eavesdropper. The transmit signal to noise ratio (SNR) at the base station (BS), transmission rates, and power allocated factors to each user are considered as main parameters. These values need be determined in design of RS-NOMA. For the first time, we analytically prove that the relay selection provides improved secure performance at higher number of relay for RS-NOMA.
- For Decode-and-Forward (DF) mode, we show that the outage behavior of RS- NOMA scheme is superior to that of OMA scheme in the specific SNR region. Furthermore, we confirm that the RS-NOMA scheme depends on how strong the eavesdropper channel is. In fact, SOP and SPSC of far user depend on the number of relay selected.
- Both analytically and numerically, the exactness of derived expressions is verified and we compare the performance of the NOMA scheme with that of the OMA scheme in the studied problems with the secrecy outage constraint.

## 2. System Model of Secure Analysis for DF Relay Selection

## 3. Secure Outage Performance in RS-NOMA

#### 3.1. SOP at D1

**Proposition**

**1.**

**Proof.**

#### 3.2. SOP at D2

**Proposition**

**2.**

**Proof.**

## 4. SPSC Analysis in RS-NOMA

#### 4.1. SPSC Compution at D1

#### 4.2. SPSC Computation at D2

## 5. Optimization and Studying OMA as Benchmark

#### 5.1. Selection of ${\alpha}_{1}$ for NOMA Transmission

#### 5.2. Asymptotic Analysis

#### 5.3. Consideration on OMA as Benchmark

## 6. Numerical Results

## 7. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Appendix A

**Proof of Proposition**

**A1.**

## Appendix B

**Proof of Proposition**

**A2.**

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**Figure 1.**System model of a RS-NOMA assisted IoT system in the existence of an external eavesdropper.

**Figure 2.**Comparison study on SOP of NOMA and OMA for User D1 versus ${\rho}_{S}={\rho}_{R}$ as changing ${R}_{1}$ (${{\lambda}_{D}}_{1}={\lambda}_{E}=1$, ${\rho}_{E}=0$ dB, ${R}_{2}=1$).

**Figure 3.**Comparison study on SOP of NOMA and OMA for User D2 versus ${\rho}_{S}={\rho}_{R}$ as changing K (${{\lambda}_{D}}_{1}={{\lambda}_{D}}_{12}={\lambda}_{SRk}={{\lambda}_{kD}}_{2}={\lambda}_{E}=1$, ${\rho}_{E}=-10$ dB, ${R}_{2}=1$).

**Figure 4.**Comparison study on SOP of NOMA and OMA for User D1 versus transmit ${\rho}_{S}={\rho}_{R}$ as varying ${\lambda}_{D1}$.

**Figure 6.**Comparison study of SOP for NOMA and OMA for User D1 versus ${\rho}_{S}={\rho}_{R}$ as varying ${\rho}_{E}$.

**Figure 7.**Comparison study of SOP for NOMA and OMA for User D2 versus ${\rho}_{S}={\rho}_{R}$ as varying ${\rho}_{E}$.

**Figure 8.**Comparison study of SOP in several cases versus ${\rho}_{S}={\rho}_{R}$ (${{\lambda}_{D}}_{1}={{\lambda}_{D}}_{12}={\lambda}_{SRk}={{\lambda}_{kD}}_{2}={\lambda}_{E}=1$, ${\rho}_{E}=-8$ dB, $K=1$, ${R}_{1}={R}_{2}=1$).

**Figure 9.**Optimal SOP in several cases with indication of optimal value regarding ${\alpha}_{1}$ (${{\lambda}_{D}}_{1}={{\lambda}_{D}}_{12}={\lambda}_{SRk}={{\lambda}_{kD}}_{2}={\lambda}_{E}=1$, ${\rho}_{E}=-5$ dB, $K=1$, ${R}_{1}={R}_{2}=0.5$).

**Figure 10.**Comparison study of SPSC in several cases versus ${\rho}_{S}={\rho}_{R}$ at D1 as setting different values of ${\rho}_{E}$ (${{\lambda}_{D}}_{1}={\lambda}_{E}=1$, ${R}_{1}=0.5$, ${R}_{2}=1$).

**Figure 11.**SPSC performance in several cases versus ${\rho}_{S}={\rho}_{R}$ as different choices of ${\rho}_{E}$ (${{\lambda}_{D}}_{1}={{\lambda}_{D}}_{12}={\lambda}_{SRk}={{\lambda}_{kD}}_{2}={\lambda}_{E}=1$, $K=1$, ${R}_{1}=0.5$,${R}_{2}=1$).

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**MDPI and ACS Style**

Do, D.-T.; Van Nguyen, M.-S.; Hoang, T.-A.; Voznak, M.
NOMA-Assisted Multiple Access Scheme for IoT Deployment: Relay Selection Model and Secrecy Performance Improvement. *Sensors* **2019**, *19*, 736.
https://doi.org/10.3390/s19030736

**AMA Style**

Do D-T, Van Nguyen M-S, Hoang T-A, Voznak M.
NOMA-Assisted Multiple Access Scheme for IoT Deployment: Relay Selection Model and Secrecy Performance Improvement. *Sensors*. 2019; 19(3):736.
https://doi.org/10.3390/s19030736

**Chicago/Turabian Style**

Do, Dinh-Thuan, Minh-Sang Van Nguyen, Thi-Anh Hoang, and Miroslav Voznak.
2019. "NOMA-Assisted Multiple Access Scheme for IoT Deployment: Relay Selection Model and Secrecy Performance Improvement" *Sensors* 19, no. 3: 736.
https://doi.org/10.3390/s19030736